But which apps are the worst offenders for killing battery life?
Here
I take some 50 of the most popular apps for the iPhone (I've excluded
gaming and camera apps because it's hard to test these in any meaningful
way), and use the built-in battery usage monitor (Settings > Battery) to keep an eye on the battery consumption.
Since
this is real-world testing, and your real-world is likely to be
different to mine (your usage is going to be different, as are other
variables such as Wi-Fi strength and such), so your mileage will
undoubtedly vary.

Facebook

Without a doubt the biggest
battery hog I've seen. Not only does it tear through the battery when
it's actively being used, but it's also a huge hog when it's in the
background too.
I knew that this would be a battery-heavy app from past experience.
I'm not a particularly heavy Facebook users and find it annoying, so I
can't imagine how bad it must be for people who are on Facebook a lot.
My advice is to either close the app when it's not in use, or prevent it from working in the background (Settings > General > Background App Refresh). Alternatively, you could access Facebook via a browser.

Google Chrome

I like Google Chrome, but I'm paying a huge battery
penalty for choosing it over Safari. Apple has done a good job of
optimizing the code in its apps. Google, on the other hand, has a long
way to go. Chrome is a solid browser, but it uses many times more power
than the built-in browser. Yes, you read that right. We're not talking
about a small difference here.
If you want the best battery life, use Safari.

Twitter

Here's
another app that not only rips through battery life while you're using
it, but it's also continually polling for new tweets when in the
background. The more people you follow, the harder the app works and the
more it hits the battery.
My advice is to either close the app when it's not in use, or prevent it from working in the background (Settings > General > Background App Refresh).

Google Maps

Another
example of being hit with a penalty for using a third-party app over
the stock app. But since the Google Maps app offers a great deal more
functionality compared to Apple's Maps app, it's not surprising that
it's such a battery hog. After all, there's no such thing as a free
lunch.

Skype

Here's another app that not only burns
through battery life during use - it's the heaviest app of its kind that
I tested - but it also continues to hammer at the battery when it's in
the background.
You could disable the app in the background, but
then you're only going to be available when the app is in the
foreground. Alternatively, if you could try to convince your
family/friends/colleagues to use iMessage and FaceTime instead.

Conclusion

Stock apps are the better choice if you want to get the most from your battery.

Social media apps are hard on the battery

Certain apps running in the background can be a real drain on the battery, so consider shutting off their access using the Background App Refresh setting.

To find out how your apps are behaving, keep an eye on the battery usage information (Settings > Battery